Online Program

Person-centered treatment (PeT) effects using instrumental variables: An application to evaluating antipsychotic drugs

*Anirban Basu, University of Washington 

Keywords: Instrumental variables, Person-centered treatment effects, schizophrenia, Passive personalization, comparative effectiveness research

Despite the goal of comparative effectiveness research (CER) to inform patient-centered care, most studies fail to account for the patient-centeredness of care that already exist in practice, which we denote as passive personalization (PP). Since CER studies describe the average effectiveness of treatments rather than heterogeneity in how individual patients respond to therapies, clinical or coverage policies that respond to CER results may undermine PP in clinical practice and generate worse outcomes.

We study this phenomenon empirically in the context of use of antipsychotic drugs in Medicaid patients with schizophrenia. We employ a newly developed instrumental variable method that builds on the methods of local instrumental variables developed by Heckman and Vytlacil (1999, 2001, 2005) and estimates person-centered treatment (PeT) effects. PeT effects are conditioned on the person’s observed characteristics and averaged over the potential conditional distribution of unobserved characteristics that lead them to their observed treatment choices. PeT effects are more individualized than conditional treatment effects from a randomized setting with the same observed characteristics. PeT effects can be easily aggregated to construct any of the mean treatment effect parameters and, more importantly, are well-suited to comprehend individual-level treatment effect heterogeneity.

In our empirical example, we find strong support for PP in clinical practice and demonstrate that the average effects from a CER study cannot be replicated in practice due to the presence of PP. In contrast, providing physicians with evidence to further personalize treatment can produce significant benefits.